The present invention relates generally to automatic nailing devices and more particularly to a nailing head assembly for an automatic nailing device.
Automatic nailing devices, such as the device disclosed in the Colson U.S. Pat. No. 3,945,549, are known in the art. These devices advantageously replace manual labor in certain repetitive manufacturing operations such as in the manufacture of pallets and wooden fencing, for example. However, the automatic nailing unit disclosed in the Colson patent has several features that limit its capacity.
The automatic nailing device of Colson forms stringer pallets and is shown in FIG. 1. The device 20 includes a frame 22 supported by a pair of vertical support legs 24 at a feed end 26, and a pair of vertical support legs 28 at a discharge end 30.
Mounted to the frame 22 is a feed conveyor 32. Although only one side of the conveyor 32 is shown in FIG. 1, the opposite side is identical, except that the opposite side is a mirror image of the side shown. Only the side shown will be described for purposes of clarity.
The conveyor 32 includes a pair of spaced apart endless chains 34, mounted on sprockets 36, 38 and 40. The sprockets are mounted onto shafts (not shown) mounted for rotation in the frame by means known in the art. A drive motor (not shown) is provided to cause the chains to move along an endless path. A plurality of drive bars (not shown) are attached at each end to the chains, and are positioned transverse to a machine direction shown by arrow 42.
A flat plate 44 is mounted to an upper surface of the frame 22 and supports a plurality of stringer magazines 46 mounted above the plate 44. Each magazine 46 drops a stringer positioned in the machine direction 42 onto the drive bars (not shown). The drive bars advance a group of stringers in the machine direction 42 in response to instructions from a controller (not shown).
A plank magazine 48 is positioned to deposit planks in a direction transverse to the machine direction 42 and onto an upper surface of each stringer. The spacing between planks and the number of planks placed on the stringers is determined by the controller (not shown).
Next, the assembly of stringers and planks is moved under a nailing station 50. The nailing station 50 includes an upright frame 52 which supports a plurality of nailing units 54. The upright frame 52 is adjustable in height to accommodate different pallet thicknesses. One nailing unit 54 is provided for each stringer.
Each nailing unit includes a vertical plate 56 and a pneumatic cylinder 58 mounted vertically to the plate. A piston 60 of each cylinder 58 is positioned on a lower end of the cylinder 58 and is fixedly connected to a driving rod 62 by means of a coupling (not shown) an upper portion of the driving rod 62 includes an enlarged portion 64 for contacting an actuator 65.
Each nailing unit includes a nailing head 66 having a vertical throughbore for accepting the driving rod 62, and a nail feed channel fluidly connected to the vertical throughbore for depositing nails into the nailing head 66. Details of the known nailing head 66 will be described in more detail below.
A vibratory nail feeder 68 is mounted to the frame 22 and is provided for delivering vertically oriented nails to a nail track 70. The nail track delivers nails to the nail delivery channel of the nailing head 66.
A cross-sectional view of the nailing head 66 is shown in FIG. 2. A nail guide track 70 comprising a pair of declining, horizontally spaced bars 72 is positioned to deliver nails to the nailing head 66. The head 66 has a main body portion 74 having a vertically oriented slot 76 extending through a side wall for receiving nails from the guide track 70. The slot 76 defines an opening to a nail feed channel 78 which delivers nails by means of gravity to a vertical throughbore 80. The throughbore 80 is substantially cylindrical and intersects and is fluidly connected to the nail feed channel 78 through an elongated opening 82. The nail drops into the throughbore 80 and continues to fall until a leading edge contacts a pair of jaws 84a, 84b pivotally mounted to the body portion 74 by means of pivot pins 86a and 86b. The jaws 84a, 84b are spring biased by means of opposing leaf springs 88a and 88b.
A tensioning device 90 is provided to adjust the amount of force delivered to the jaws 84a, 84b by the leaf springs 88a, 88b. The tensioning device comprises a housing 92, a spring 94 and an adjustment knob 96 for adjusting the amount of force the spring 94 applies to the leaf springs 88a, 88b.
A driving rod 62 is driven downwardly by means of a hydraulic ram 60 (shown in FIG. 1) to force a nail which is retained in a lower portion of the throughbore 80 through the spring biased jaws 84a, 84b and into the materials to be nailed together (not shown) located beneath the jaws 84.
A nail picker plate 98 is mounted for horizontal, reciprocal sliding motion in the nailing head 66. The direction of motion of the picker plate is into and out of the paper. A top elevational view of the picker plate is shown in FIG. 3.
The picker plate has a first major surface 100, an opposite surface 102 (shown in FIG. 2) substantially flat edges 104, 106 and 108, and a cammed edge 110 for contacting a cammed surface on an actuator (not shown). The picker plate has a notch 112 for receiving a nail picked from the nail track 70. The picker plate also has an aperture 114 extending through the first and opposite major surfaces 100 and 102. Connecting the aperture 114 and the notch 112 is a channel 116 which permits the nail in the notch to move to the aperture. The notch is smaller in width than the nail head, and the nail is suspended in the slot 76 of the main body portion when positioned in the notch 112.
An actuator (not shown) causes the picker plate 98 to move in a direction shown by arrow 118 when a lower shoulder (not shown) on an enlarged portion 64 of the nail driving rod 62 contacts an upper surface of the actuator (not shown). A camming surface of the actuator which contacts camming surface 110 causes the picker plate to move in a direction shown by arrow 118 until a leading edge of the notch 112 is aligned with an open end of the nail track 70. The vibration of the nail feeder 68 and nail track 70 causes the nail to travel into the notch 112. This occurs as the driving rod 62 nears the lowest portion of the downstroke. As the driving rod 62 begins moving upwardly, the actuator releases pressure on the camming surface 110 and the picker plate 98 moves in a direction opposite the direction shown by arrow 118. During this portion of the movement, the picked nail moves through the channel, and into the aperture 114. The aperture is larger than the size of the nail head and the nail falls through the aperture into the nail feed channel 78 (shown in FIG. 2).
Referring back to FIG. 2, the nailing head 66 as well as the hydraulic cylinder 58 (shown in FIG. 1) are mounted onto the vertical plate 56. The vertical plate 56 is removably attached to the frame by means of an upper pair of horizontally positioned channel members (not shown) and a lower pair of horizontally positioned channel members 119a and 119b which are fixedly mounted to the vertical portions of the upright frame 52 (shown in FIG. 1).
The nailing head 66 is formed from a back section 120 having a vertical, cylindrical groove defining part of the inner surface of the throughbore 80. The head also has a lower front portion 122 having a vertically oriented cylindrical groove defining a portion of the throughbore and a portion of the nail feed channel 78. The head also has an upper front portion 124 having an inner throughbore defining a portion of the nail feed channel 78. Although these parts can be disassembled with the use of tools, it is time consuming and difficult to take the nailing head 66 apart to clear the throughbore 80 and nail feed channel 78 of nails plugging the passages. When the nail head is in a central portion of the nailing station, this task becomes particularly difficult, and causes production delays.
A disadvantage of the device shown in the Colson patent is that a nail is not positioned in the notch of the picker plate until the driving rod is nearing the bottom of the downstroke. Because the picker plate is only in a position to pick a nail for a small portion of the nail hammering shaft's stroke, the picker plate does not always receive a nail from the nail guide track 70. The presence of substances such as galvanized coatings on the nails that cause the nails to stick together may aggravate this problem. Accordingly, the operating speed of the known automatic nailing device is limited.
Another disadvantage is that the nails do not have sufficient time to fall from the picker plate to the bottom of the nail driver bore at higher production rates. The descent of the nail is slowed when the nail is making the transition from the nail feed channel to the throughbore, because the nail must change direction abruptly at the intersection of the nail feed channel and the throughbore. Accordingly, the operating speed of the known automatic nailing device is limited.